Progress on the presents client.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3848 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/presents/net/UpstreamMessage.as

@@ -0,0 +1,48 @@
+package com.threerings.presents.net {
+
+import com.threerings.io.Streamable;
+
+public class UpstreamMessage
+    implements Streamable
+{
+    /** This is a unique (within the context of a reasonable period
+    * of time) identifier assigned to each upstream message. The message ids
+    * are used to correlate a downstream response message to the 
+    * appropriate upstream request message. */
+    public var messageId :int;
+
+    /**
+     * Construct an upstream message.
+     */
+    public function UpstreamMessage ()
+    {
+        // automatically generate a valid message id
+        this.messageId = nextMessageId();
+    }
+
+    // documentation inherited from interface Streamable
+    public function writeObject (out :ObjectOutputStream) :void
+    {
+        out.writeShort(messageId);
+    }
+
+    // documentation inherited from interface Streamable
+    public function readObject (ins :ObjectInputStream) :void
+    {
+        messageId = ins.readShort();
+    }
+
+    /**
+     * Returns the next message id suitable for use by an upstream message./
+     */
+    protected static function nextMessageId () :int
+    {
+        _nextMessageId = (_nextMessageId + 1) % JavaConstants.SHORT_MAX_VALUE;
+        return _nextMessageId;
+    }
+
+    /** This is used to generate monotonically increasing message ids on the
+     * client as new messages are generated. */
+    protected static var _nextMessageId :int;
+}
+}